Yes.
Your calculations would be correct for an ideal opamp having infinite gain and infinite input impedance. The results are a very good approximation to reality. However, to answer question 1 correctly you need to take into account both the actual input impedance and the finite gain as per spec. Draw out the circuit, including the input impedance, to see how that affects things.

Edit:
I'm unclear why you're told the amp 'has a gain of 15', and then in (i) you are asked to 'determine the closed loop voltage gain' ?